a) Field of the Invention
The present invention relates to a pump and more specifically a compact decompression pump which utilizes a diaphragm.
b) Description of the Prior Art
As a conventional example of decompression pump which uses a diaphragm, there is known a pump disclosed by Japanese Patent Kokai Publication No. Hei 6-147128.
This depression pump has a configuration shown in FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are a sectional view and a partially enlarged view thereof, wherein a reference numeral 1 represents a driving motor, a reference numeral 2 designates an output shaft of the motor, a reference numeral 3 denotes a crank base fixed to the output shaft, a reference numeral 4 represents a driving shaft which is studded on the crank base 3 in a condition inclined to the output shaft 2, a reference numeral 5 designates a disk like driving body which is rotatably mounted on the driving shaft 4, and a reference numeral 6 denotes a plurality of pistons which are arranged at equal intervals on circumferential portions of the driving body 5 and reciprocally movable in a plurality of pump chambers 7 which are arranged along a circumference of the driving body 5. A reference numeral 8 represents a diaphragm which connects the pump chamber 7 and the piston 6 so as to maintain the pump chamber 7 in an airtight condition, a reference numeral 9 designates an inlet port which is communicated with the pump chamber 7 by way of a check valve 11, and a reference numeral 10 denotes an exhaust port which is communicated with the pump chamber 7 by way of a check valve 15. The diaphragm 8 has a U sectional shape having a convexity 8a which protrudes toward the pump chamber as shown in FIG. 1 and FIG. 2. The convexity 8a forms as a whole an annular portion which surrounds the piston 6 and is disposed so that its inside surface and its outside surface are kept at least partially in contact with an outer circumferential surface of the piston 6 and an inside surface of the pump chamber 7 respectively. Accordingly, the diaphragm is not deformed unnecessarily due to decompression in the pump chamber whether the piston 6 is positioned at a left side piston location in FIG. 1 or a right side piston location in FIG. 1 (the piston location shown in FIG. 2), whereby this diaphragm is preferable for use in a decompression pump.
In the diaphragm pump which has the configuration described above, however, a narrow portion 8c exists between the diaphragm 8 and the piston 6 since the diaphragm 8 which allows the reciprocal motion of the piston 6 while maintaining it in an airtight condition has the U shape sectional shape and is molded integrally with the piston 6 as shown in FIG. 1. Accordingly, a metal die is liable to be deformed at a stage to integrally mold the diaphragm 8 and the piston 6a since a narrow portion (thinned portion) is formed also in the metal die. FIG. 3 shows an outline (a shape of a surface on which a molding is located) of a metal die which is used to integrally mold the diaphragm 8 and the piston 6. An elongated portion which is to form the narrow portion described above is liable to be deformed or broken and it is impossible to maintain the metal die in a desired form for a long time, thereby making it difficult to perform mass production of the diaphragm pump.